Holograms are becoming increasingly well known and used in a variety of fields. For example, due to the level of technological sophistication required to produce them, holograms have found significant application for verifying the authenticity of documents like credit cards. Besides being difficult to produce and/or duplicate, holograms have intrinsic aesthetic and functional attributes which render them interesting and appealing to those who view them. In the first instance, the hologram has the capacity to reconstruct a three dimensional image from a two dimensional surface. Further, holograms typically have unusual brightness and coloration which changes with viewing and illumination angle.
Over the years, techniques have been developed for mass-producing low cost holograms, so that their aesthetic attributes can be widely utilized. For instance, holograms are now mass-produced by embossing coated plastic film in web form. Because holograms are interesting and attractive and because methods for economically producing holograms on a large scale have been devised, they have come to be used for packaging and marketing purposes on mass-produced materials and products, such as greeting cards, magazine covers and compact discs. As applied to such marketing and decorative tasks, holograms have certain limitations. For instance, lighting must be provided at a specific orientation and angle to reconstruct the hologram effectively. By way of example, the image should be arranged in an erect orientation and illuminated at 35 degrees relative to the surface of the hologram. Of course, optimum viewing angle and orientation are dependent upon corresponding exposure parameters.
When a hologram is viewed or illuminated at non-optimal angles, the resultant image is degraded in quality and is essentially non-viewable at certain angles and in certain lighting conditions. Since a hologram applied to a product or publication is not guaranteed optimal lighting during the commercial life of the product (e.g., during display on a shelf in a store or newsstand, or sitting on a consumer's coffee table at home), it is likely that a significant portion of the holographic effect will go unappreciated due to uncontrollable marketing and use conditions. As a result, the hologram will not be enjoyed to the maximum extent possible and will not have a maximum commercial impact.
Prior to the popularization of holograms, diffraction gratings embossed in metallized plastic films and other substrates have been used to provide a bright and interesting surface treatment. As is known, diffraction gratings may be produced optically by the interference pattern of a plurality of intersecting beams or mechanically by a ruling engine. Diffraction gratings exhibit brightness and color change with changing viewing angle and therefore are popular for decorating such items as greeting cards, gift wrap, lighters and numerous other products.
While diffraction gratings exhibit color change, they do not convey any three dimensional information. A surface treatment utilizing discrete areas of diffraction gratings disposed at varying selected orientations is disclosed in U.S. Pat. No. 5,158,845 to Waitts, et al. and assigned to the assignee herein, Crown Roll Leaf, Inc. In accordance with the '845 Patent, areas of a substrate which are embossed with a diffraction grating at different orientations (and potentially in different shapes as determined by associated dies) display color changes offset from that of neighboring areas. In this manner, the substrate has a brighter and more interesting diffractive pattern than could be realized using a diffraction pattern arranged at one angular orientation.